Simply adding or identifying “corridors” does not necessarily achieve connectivity. Connectivity is a measure of how well organisms can move through the landscape. The spatially mappable connections in the landscape are better referred to as connectedness and do not necessarily indicate connectivity.

The objective of conserving or repairing connectivity is to ensure population survival. Populations in most environments are composed of a mosaic of subpopulations. The subpopulations each may become locally extinct, i.e. decrease to zero, but with adequate connectivity the population of the entire mosaic of subpopulations, can survive with greater certainty.

This is so because for every subpopulation patch that goes extinct, an empty patch is recolonized. The rate of local extinction of subpopulations is matched by a rate of recolonization of local extinctions. This recolonization is possible only if the landscape allows the animals or plants to move freely among the habitat patches that support the subpopulations. This process can be especially important in landscapes where the total amount of habitat has been much reduced.

In many environments, particularly those heavily used by humans, the habitat is very fragmented. In the extreme, the native habitat between subpopulations is replaced by unnatural, often threatening or dangerous habitat. For example, squirrels may be confined to isolated patches of woods because lack of trees in intervening habitats prevents movements by the squirrels. Movement can be even more difficult for some plants. Trout lilies move mainly by extension of underground rhizomes. Unless there are small populations surviving in farm fencerows, trout lilies in farm woodlots are usually completely isolated in each woodlot. In such cases, connections between patch populations will need to be breeding habitat, not just spatial corridors.

Research has not clearly separated the effects of lack of connectivity from the effects of loss of usable habitat as the major cause of local extinctions of patchy populations.

With intense fragmentation, humans also commonly may insert barriers, such as highways, gravel pits or strip malls, between the subpopulation patches thus increasing the isolation.

If the organisms can’t move among the patches and patches emptied by local extinction are not recolonized, the number of empty patches will continue to increase until the species is extirpated over the entire region.

Programs attempting to conserve connectivity need to consider how quality, extent and spatial distribution of habitat affect movement behaviour in particular species. White-footed mice will use farm fields, even plowed corn fields, as breeding habitat and will move across them between patches of their usual wooded habitat. But chipmunks in that same farmland will not use farm fields and can be isolated in farm woodlots simply by lack of woody fencerows. Because they can fly, it often is assumed that birds and damselflies are unaffected by spatial distribution of habitats on the ground. But, during breeding season, some birds are unwilling to fly across open areas without any treed way-stations. Some damselflies use watery habitats for breeding but adults must be able to fly to mature woodland for foraging.

Relationships between life history patterns and movement behaviour can be critical to population survival and must be considered in landscape planning and stewardship. Trained ecologists, biologists and natural historians should oversee and evaluate computer programs and engineered landscape changes so that conservation of connectivity is understood as movement of organisms that increases the probability of population survival.

Increasing the amount of habitat between patches will both relieve any problem of habitat shortage and also will improve the connections among patches and both will increase the probability of population survival.

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